Abstract:
The orthophoto mosaic is a rectified georeferenced image of the Heard Island, Laurens Peninsula Coastal Area. Distortions due to relief and tilt displacement have been removed. Orthophotos were derived from non-metric cameras (focal length unknown).

Quality
This mosaic was created from a series of photographs covering the coastline of the Laurens Peninsula captured during 1980 using a Hasselblad camera: film CASC9495 frames 51-56 and 58-60. A single photo captured using a Linhof camera in 1987/88 was also used: film ANTC1210 run 2 frame 182. Dr Jenny Scott visited Heard Island during 2000 to conduct vegetation surveys. ... Dr Scott used the photography as a base for her mapping and also used a global positioning system to coordinate control points in the photography. A digital elevation model was obtained from Radarsat using 1997 radar imagery. The aerial photographs were ortho rectified using the ground control obtained by Dr Scott, and additional derived points read off the Orthorectified Digital Globe image for Laurens Peninsula, and the digital elevation model obtained from Radarsat. The inner orientation parameters for the cameras were unknown but the focal length was derived by first measuring the diagonal distance across the negative (this gave an approximate focal length). The final value for the focal length was computed using the ERDAS OrthoBase Pro Self Calibrating Bundle Adjustment software. The focal length adopted for the camera was 82mm. The ERDAS software was used to perform a bundle adjustment on the photography using the ground control and tie points. The bundle adjustment resulted in average RMS errors of +/-6m in position and height (XY and Z). For the residuals from the adjustment refer to the PDF available for download (see Related URL below). Each image was then ortho rectified using the orientation parameters derived from the bundle adjustment and the Radarsat DEM. The orthorectified images were then joined to form an image mosaic for the Laurens Peninsula. The image mosaic was not colour balanced. The pixel size on the ground for each image is 0.82m. The image was projected to UTM Zone 43 (WGS84). The adjustment accuracies achieved with aerial triangulation however are not indicative of the true position of the images. The following factors affect the absolute position of the images: 1- The focal length used for the camera is only an estimate. It is not possible to perform an accurate calibration of the camera from the supplied ground control points. This will have a direct effect on the initial scale of the images which could result in some distortion of features. 2- Not all the coordinated Ground Control Points could be used in the adjustment. 3- The overlap of the images is minimal on some images. This makes the aerial triangulation process less robust. 4- Cloud cover on the images makes the location of tie points between images difficult, narrowing the range in which they can be placed. Hence although the adjustment accuracy is to within +/-6m the absolute position of the mosaic is only +/- 160m The coverage of the aerial photos is shown by the polygon shapefile available for download (see Related URL below).

Access Constraints
Contact the technical contact at the AADC for access to the data. Access is restricted due to the size of the mosaic. The mosaic will be made available on CD. The mosaic is in ERDAS Imagine format and is 582 Mb.